Freescale 1.2KW SSPA for 144 MHz

As previously described in the zl4plm.com article on the 1KW Freescale amplifier, these rugged 50V LDMOS FETs are providing a useful addition to the amateur fraternity.

They offer a very easy way to generate power at levels between 300 and 1000W and are relatively simple designs to build and intergrate in a VHF-UHF station. Additionally new designs are appearing on a regular basis on the Internet and in specialist magazines such as DUBUS.

The previous 1KW device while generating a significant power and more than adequate, is not the highest power level these devices offer. For the ultimate power amplifier using a single non-combined PA, Freescale offer the next step up, the MRFE6VP61K25H. This top of the line device offers 1.25KW out across the HF-600 MHz range and like its brothers and sisters, is a robust device capable of handling some significant abuse.

The 1.25KW level is useful here in NZ as it allows me to run 1KW at the antenna with some headroom for small losses associated with connector/cable losses. The MRFE6VP61K25H is a drop is replacement for the 1KW sized V11P device too, it needs no retuning or changes in the circuit. It has the same device footprint too so it can be dropped into the same PCB layout. The only drawback ... price! It is significantly more expensive than the 1000W level, something to consider, but I was looking for 1KW out at the antenna so the extra headroom was attractive.

Construction is exactly the same as the 1KW device so please read the information in that article before you attempt this project.

The RF pallet is constructed in the same PCB - so you can buy the same RF parts kit from RFham in France. The PCB and heatspreader are mounted exactly the same way. In this version I soldered my PCB to the heatspreader. As I said in the 1KW article this causes all sorts of construction issues. I saw no performance loss and Jim W6PQL also bolted his PCB down without issue, I would say there is no benefit and it causes a whole raft of things to work round later. Stick with bolt down is my advice.

You can see the soldering detail on the image to the left here. The device is mounted in the same way as the 1KW by soldering down. You can also see the input balun at the bottom right and the output baluns constructed from the white teflon coax.

The remainder of the construction is the same and testing follows exactly the same approach as the 1KW pallet. I would only recommend that you take alittle more care in testing regards heat dissipation.

Power supply requirements are similar to the 1KW level - 50V at approximately 35A. I used the same bias mods as per the 1KW article and set the standing current to 2A. This sets the PA in Class AB and allows it to run SSB, CW or digital modes. Of course if you are only interested in JT65 you can set the amp for Class C and reduce heating etc, but as I like my amps to be as flexible as possible so I leave mine in Class AB.